Sealants used in aerospace and other applications must satisfy demanding mechanical, chemical, and environmental requirements. Sulfur-containing prepolymers such as polysulfides and polythioethers are suitable for use in aerospace sealant applications. Thiol-terminated sulfur-containing prepolymers can react with a curing agent in the presence of a catalyst to provide cured sealants. Many aerospace sealants exhibit a long working time such as from 2 hours to 48 hours, and an even longer curing time, for example, up to 56 days. In certain applications it is desirable that a curable sealant composition have a long working time such as from 2 days to 10 days and short cure time such as less than 2 days. Although an increased amount of catalyst may be added to shorten the curing time, even in small amounts a catalyst can have a detrimental effect on the properties of the cured sealant. For example, amine catalysts used in thiol-epoxy curing chemistries and oxidants such as manganese dioxide used in thiol-condensation curing can reduce the tensile strength and elongation of the cured sealant.
Therefore, it is desirable to develop improved catalyst systems for use with thiol-terminated sulfur-containing prepolymer compositions that exhibit an extended working time, a fast cure rate, and provide a cured sealant exhibiting acceptable performance for aerospace applications.